The use of methylpolysiloxanes for defoaming liquids is one of the first areas in which these products were used. There exists a large number of publications and patents wherein the mode of action of the siloxanes is described, and advice is given for selecting suitable siloxanes and the forms in which they are prepared.
It was already recognized earlier that the use of mixtures of different polysiloxanes can be advantageous. For this purpose, a large number of different organofunctionally-modified polysiloxanes have also been developed. A typical organofunctional group, which modifies the properties of the polysiloxanes, is the polyether group with oxyethylene and/or oxypropylene units. In the course of further development, polysiloxanes, with combinations of polyether groups of different hydrophilicity, were used for the modification. Finely divided, mostly pyrogenic silica, which is optionally used in the hydrophobized form, is an important component of such defoamer emulsions based on polysiloxanes.
From the large number of Offenlegungsschriften and patents relating to defoamers based on polysiloxanes, the following publications are cited as examples:
U.S. Pat. No. 3,984,347 relates to a preparation, which consists essentially of:
1. 50 to 98.9% by weight of a basic oil, which is a polyoxypropylene or a polyoxypropylene-polyoxyethylene polymer with a molecular weight of 500 to 6,000, or a siloxane glycol polymer of the general formulae
(a) (R.sub.a Si(OSiMe.sub.2).sub.n (OSiMeG).sub.b OSiMe.sub.2 G).sub.4-a, PA1 (b) (R.sub.a Si(OSiMe.sub.2).sub.n (OSiMeG).sub.r OSiMe.sub.3).sub.4-a, PA1 (c) GMe.sub.2 Si(OSiMe.sub.2).sub.n (OSiMeG).sub.b OSiMe.sub.2 G), or PA1 (d) Me.sub.3 Si(OSiMe.sub.2).sub.n (OSiMeG).sub.r OSiMe.sub.3 PA1 R is a hydrocarbon with 1 to 10 carbon atoms, free of olefinic double bonds, PA1 Me is a methyl group, PA1 G is a group having the formula --D(OR').sub.m A, in which D is an alkylene group with 1 to 30 carbon atoms and R' is an alkylene group with 2 to 10 carbon atoms, m has a value of at least 1 and A is a capping group, PA1 a has a value of 0 or 1, PA1 n has a value of at least 12, PA1 b has a value of 0 to 50, and PA1 c has a value of 1 to 50; PA1 5 to 10 parts by weight of silica and 0 to 20 parts by weight of a siloxane resin, which consists essentially of the units SiO.sub.2 and (CH.sub.3).sub.3 SiO.sub.1/2 in the ratio of 1:0.4 to 1:1.2; and PA1 i) a polydimethylpolysiloxane-polyether copolymer, in which the molecular weight of the polysiloxane is at least 2,000, and the polyoxypropylene polymer has a molecular weight of at least 800, or a polyoxyethylene-polyoxypropylene copolymer with a molecular weight of 1,500, the polyether being linked over an SiC bond to a silicon atom of the siloxane, or PA1 ii) a polydimethylpolysiloxane-polyether polymer, which is obtained by heating a mixture of a methyl-hydrogenpolysiloxane having a molecular weight of at least 1,500, and a polyoxypropylene glycol having a molecular weight of at least 800, or a polyoxyethylene-polyoxypropylene glycol having a molecular weight of at least 1,500. PA1 a) a liquid or organopolysiloxane with at least one hydroxyl and hydrocarbon group, PA1 b) a silicone resin or a compound producing a silicone resin, PA1 c) a finely divided filler, and PA1 d) a catalyst for the reaction between a) and c), the secondary defoaming ingredient being a mixture of a liquid methylpolysiloxane, at least one nonionic silicone surfactant, a first organic dispersant and a second dispersant, based on a nonionic difunctional block copolymer with terminal primary hydroxyl groups. PA1 R.sup.2 is a hydrogen group or an alkyl group with 1 to 8 carbon atoms, PA1 Z is a divalent group having the formula --O--, --(CH.sub.2).sub.p --O-- or --CH.sub.2 --CH(CH.sub.3)--CH.sub.2 --O-- with p=2 or 3, PA1 n has an average numerical value of 2.7 to 4.0, PA1 m has an average numerical value of 5 to 130, PA1 R.sup.2 and Z have the meanings already given, PA1 q has an average numerical value of 2.0 to 2.7, PA1 r has an average numerical value of 5 to 120, PA1 g has an average numerical value of 4 to 200, PA1 h has an average numerical value of 0 to 100, and PA1 j has an average numerical value of 0 to 50; and PA1 x=2.6 to 30, preferably 2.8 to 3.0; PA1 y=8 to 80, preferably 20 to 60; PA1 w=7 to 50, preferably 13 to 30; and PA1 z=1.5 to 0, preferably 1.5 to 5.
wherein
2. 1 to 40% by weight of a defoamer, which is obtained essentially from 88 to 95 parts by weight of a liquid polydimethylsiloxane with a viscosity of at least 20 cSt at 25.degree. C.,
3. 0.1 to 10% by weight of a dispersant, which disperses component 2 in component 1 and is a siloxane copolymer, which either is
The published European patent application 0 354 016 relates to a textile detergent which contains raw detergents, builders and at least one material for controlling the foam, with the distinguishing feature that a dispersable preparation of a silicone defoamer is contained in the detergent and consists of a non-aqueous emulsion of a primary and a secondary defoamer, the primary defoaming ingredient being a mixture of:
Finally, reference is made to the published European patent application 0 427 263, in which a silicone-based defoamer preparation is described, which contains (i) a polydiorgano-siloxane, (ii) silica, and (iii) 4 to 2500 parts by weight, based on 100 parts by weight of the sum of components (i) and (ii) of a modified silicone oil, the molecule of which has at least one functional organic group which is linked to a silicon atom, as well as at least one epoxy, amino, amide, carboxyl, alkoxyl or hydroxyl group, and at least one optionally substituted polyoxyalkylene group which is linked to a silicon atom.
Even though these known defoamers can be used advantageously to prevent or eliminate foam in aqueous systems, unfulfilled or inadequately fulfilled requirements, nevertheless, remain.
One of these requirements is to prepare defoamer emulsions which are as concentrated and stable as possible and can be diluted by the user to the desired concentration, while retaining the stability of the emulsions. This is possible with simple stirring equipment without requiring expensive stirring technology or special precautions. At the same time, the diluted emulsions must satisfy high stability requirements and should exhibit high stability particularly when subjected to temperature changes and to shaking. It is, therefore, an object of the invention to solve this technical problem.